One of my smaller discus - probably around 2-3 inches - has stopped eating all of a sudden. I have recently introduces co2 into the tank and I figured it was stress that caused him to darken and separate from the rest. I have successfully introduced co2 into a discus tank in the past and I was aware of doing this very slowly - one bubble per second. I have also carried out extra water changes to help acclimate the fish slowly.

However this particular fish went on a hunger strike very soon. As soon as I began noticing symptoms, I quickly quarantined him into a 6 gallon hospital tank and treated him with 60% water changes, aquarium salt and methylene blue for three days. I have also bumped up the temp to about 32 C (89.6 F) and he seemed to be getting better. He swims normally and came to greet me every time I was near, but still didn't eat anything. I moved him back into the main tank because I figured it could be the isolation which was preventing from eating.

After he was back he rejected the Tetra Bits that they love so much and only ate algae. He mostly just hid in the corner, away from the other fish and occasionally munched on algae. I moved him back again into isolation yet again and am currently treating him with epsom salt and metro. His poop seems normal - it was solid and green in colour.

Its been three days since I began the metro treatment. I keep the protected from light and I dose about 300mg of metro with 70-80% and about half a teaspoon of epsom salt every 24 hours.

I unfortunately have no means of testing my water parameters, it is extremely expensive and rare to find a test kit in Dhaka (Bangladesh) but I religiously keep my tank clean with 30-40% water changes weekly. I have rarely ever had fish my die/get sick and as the rest of the school is still thriving - I keep 5 discus in a 66 gallon planted tank - I can say with certainty that its not the water that is the issue.

I am guessing it could be a case of Hex - all the symptoms match except the white stringy poop. But I'm afraid could be wrong. I have little to no experience of treating fish and if anyone can share their knowledge and help me get a proper diagnosis, I will be forever grateful.